Anti-semitism spreads like any other viral mass delusion--asset bubbles (and busts), 17th century witchhunts and trials, Fuhrer cults. The uniqueness of anti-semitism is:

1. It's a theory of how conspiratorial power in the world works.

2. It has no geographical limits. Hatred of gypsies in Slovakia won't spread to Australia or Chile. But the seeds of Jew hatred know no such geographical limits because the sacred texts of Christianity and Islam, both of which contain Jew hatred, are embedded in or imported into almost every culture in the world.